MediaTakeOut.com has received CONFLICTING REPORTS from a number of very CREDIBLE INSIDERS which suggest that Rihanna and Matt Kemp may have gotten into an ARGUMENT - which caused them to miss Rihanna's BEST FRIEND Katy Perry's wedding.

Here's what we know. As we reported to you earlier, Rihanna and Matt Kemp have been FIGHTING recently. Well the two decided to take a PRIVATE TRIP to Mexico earlier this week. The plan was to stay there until FRIDAY, when they'd fly to India for Katy's wedding.

Well it didn't work out that way. A person very close to Rihanna told MediaTakeOut.com, "[Rihanna] and Matt were [verbally] fighting all week, and it ended up messing up their plans." The insider continued, "I'm worried about Rihanna."

We're worried TOO. As we told you before, Matt Kemp got BUSTED for beating up an EX-Girlfriend (Read Here). And Rihanna, well, you know she likes to get it in.